Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (23,687)	$ (13,206)
Other comprehensive gain (loss):
Net unrealized gain (loss) on available-for-sale securities	106	(56)
Total comprehensive loss	$ (23,581)	$ (13,262)